What is a Riving Knife on a Table Saw?

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We all know a table saw has a blade.  Duh?  The home woodworking enthusiast also knows the blade turns toward you as you push the wood through it for your cut.

But just as that branch will close in on your tree saw as you cut through it, so will wood as it is cut on your table saw.  Your table saw, though, is much stronger than you are, and the blade will grab the wood, lift it and kick it back at you.  Serious injury can result, and perhaps you’ve even had it happen to you or someone you know.

Fortunately, a riving knife will prevent this from happening.  A riving knife?  But I have a saw, so why do I need a knife, too?

Do I Need a Riving Knife On My Table Saw?

Riving Knife

Before answering, let’s make clear what a riving knife is.

It’s a safety device that is attached to the table saw’s arbor – the shaft that holds the blade – in a fixed position relative to the blade so that as the blade is raised and lowered, the riving knife moves in unison with it. 

If we return to the image of that branch that closes on your tree saw as you cut through it, we know if we pull the branch on the outer side of the cut downward, it widens the kerf – the width of the cut – and makes cutting easier.  This is what a riving knife does on your table saw.

It keeps the kerf on the wood piece open and prevents the cut from closing around the rear teeth of the blade.  It is an anti-kickback device, if you will, that keeps the kerf open, so it is not grabbed by those rear teeth and sent back at your face.

For this safety reason, of course, your table saw should have a riving knife. However, it is now even required.  Since 2009, Underwriter’s Laboratory (UL) has mandated that all table saw designs, whether cabinet or portable, include a riving knife.

For non-through cuts, those that simply make a slot in the wood, such as with the use of dado blades, a riving knife is not necessarily needed.  There is no kerf to maintain, and the workpiece will not be grabbed by the blade and sent back at you. When using such a blade, and where a riving knife serves no purpose, the riving knife should be removed from the arbor. 

Otherwise, yes, you need the safety provided by a riving knife to keep your face pretty and your head uninjured.

How Thick Should The Riving Knife Be?

You don’t want the kerf to be widened while the wood piece is being cut, as it can affect the cut by splitting or binding the wood.  So, your riving knife, usually made from steel, should be a bit thinner than the blade.  This will allow the smooth passing of the wood beyond the blade and the knife and, in turn, the smooth and steady cut of the wood.

Riving Knife Thickness

The riving knife will be held in a fixed position relative to the blade, so the distance between the blade and the riving knife will remain constant.  That distance will not be great, either, so the protection afforded by the knife will also be consistent.

What Is The Difference Between a Riving Knife and a Splitter?

The constancy of the distance between a riving knife and the blade is its advantage over a splitter.  While both a riving knife and a splitter are designed to keep the kerf open as the wood is passed through the blade, the riving knife is always kept a fixed distance from the blade, usually no more than ⅜”, as contrasted with a splitter that can sometimes be more than an inch or two from it.  This is because of the way a splitter is attached to the arbor.

For added measure, and as we mentioned, the riving knife will rise and fall in unison with the blade as you move it, and the fixed distance remains constant.  The splitter is stationary, and so the distance between it and the blade is not constant.

As between the two, for the extra safety precaution, be sure to opt for the riving knife.  Today’s table saws make that choice for you, as riving knives are required in table saw design, whereas splitters are not.

What’s The Difference Between a Riving Knife and An Ordinary Table Saw Blade Guard?

We already know what a riving knife is and why your table saw needs one.  But what about the saw blade guard?

The saw blade guard is exactly what the name implies – a device that guards the blade.  It prevents wood from falling on the spinning blade, among other things.  While the saw blade guard won’t necessarily keep your fingers safe from the blade, it is a good reminder to keep them away from the blade when the saw is on. 

Each is a safety device for your table saw, but they serve different purposes.  We certainly recommend using every safety device available for table saw use.  Your fingers, face, and head are important to you, and these two devices are intended to protect them to one degree or another.  And, be sure to add safety goggles to that list, also.

Finally, as for riving knives, don’t use your table saw without one.  It is not absolute protection from kickback, but it reduces the possibility significantly. 

When coupled with good table saw practices all around, your safety can be maximized.

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